Golf club shafts

Abstract

A tubular blank for producing golf club shafts comprises a butt section having a uniform cross-sectional configuration along its length, a tip section also having a uniform cross-sectional configuration along its length, and a tapered section interconnecting the butt and tip sections. Metallurgically formed rifling on the interior surface of the blank extends throughout the entirety of the butt, tip and tapered sections. The golf club shafts produced from these blanks have increased strength and stiffness which is a direct result of the interior rifling. A set of golf club shafts preferably is produced from a group of these tubular blanks with each blank of the group having the same length and the same natural frequency. Predetermined portions are then selectively removed from the tip and butt sections. The ultimately produced golf club shafts are frequency matched along a predetermined gradient and each shaft of the set has a predetermined stiffness distribution along its length directly related to the stiffness distribution of the other shafts of the set.

What is claimed is: 
     
       1. A golf club shaft, comprising; a tubular blank having a continuous exterior surface, and an interior surface along its length, a butt section having a given outer diameter, a tip section having a given outer diameter smaller than the outer diameter of the butt section, a tapered section interconnecting the butt and tip sections, and metallurgically formed rifling on the interior surface of the blank extending throughout the entirety of the butt, tip and tapered sections, said metallurgically formed rifling comprising a plurality of alternating longitudinally extending lands and grooves wherein the depth of said grooves does not exceed the widths of said lands, and wherein the lands and grooves in the tip section are parallel to each other and the lands and grooves in the butt section are parallel to each other. 
     
     
       2. A golf club shaft as in claim 1 wherein the longitudinally extending lands are equally spaced apart and the longitudinally extending grooves are equally spaced apart at any given diameter. 
     
     
       3. A golf club shaft as in claim 2 wherein the butt and tip sections have a common central longitudinal axis and wherein the alternating longitudinally extending lands and grooves in the butt and tip sections are parallel to the common central longitudinal axis. 
     
     
       4. A golf club shaft as in claim 1 wherein the metallurgically formed rifling includes at least eight lands and at least eight grooves extending throughout the entirety of the butt, tip and tapered sections. 
     
     
       5. A golf club shaft as in claim 1 wherein each longitudinally extending land includes a plateau spaced approximately 0.008 inch from the adjacent longitudinally extending grooves. 
     
     
       6. A golf club shaft as set forth in claim 1, wherein said exterior surface is smooth and substantially uninterrupted. 
     
     
       7. A method of making a tubular blank from which a golf club shaft is produced comprising the steps of; forming a tube having a constant cross-sectional configuration along its length, positioning a plug mandrel inside the tube, the plug mandrel having alternating parallel longitudinally extending lands and grooves on an outside surface thereof, drawing the tube over the plug mandrel to metallurgically form rifling on the inside surface of the tube in the form of a plurality of alternating longitudinally extending parallel lands and grooves corresponding to the lands and grooves on the plug mandrel, cutting the tube into desired lengths, and swaging each length of tube to form tip and butt sections and an interconnecting tapered section, the lands and grooves of said butt section being parallel to each other, and the lands and grooves of said tip section being parallel to each other, and said tip section having a diameter smaller than the diameter of the butt section.   
     
     
       8. A method of producing a frequency matched set of golf club shafts from a plurality of oversized tubular blanks, each shaft in the set having a stiffness distribution directly related to the stiffness distribution of the other shafts in the set such that each successive shorter shaft has an increased stiffness along a predetermined gradient, each blank having a tip end section and a butt end section and an intermediate tapered section, the method comprising the steps of; selecting a plurality of oversized blanks equal in number to the number of shafts in the set, each blank having substantially the same natural frequency and length, each blank having metallurgically formed rifling to define a plurality of alternating longitudinally extending parallel lands and grooves on an interior surface of said tip section and of said butt section, removing a predetermined portion of length from the rifled tip end section of each blank and a constant additional length differential of tip end removal between said successive blanks of the plurality of said blanks to produce a set of golf club shafts with said constant length differential of overall length between successive shafts of the set.   
     
     
       9. A method as in claim 8, wherein each of the oversized tubular blanks of the plurality selected has substantially the same natural frequency ±two cycles per minute, and removing a predetermined portion of constant length from the butt end section of each blank. 
     
     
       10. A method as in claim 8 including the step of fitting selected golf club heads to the set of golf club shafts. 
     
     
       11. A method according to claim 8, wherein said constant length is one half inch. 
     
     
       12. A method of producing a set of matched golf club shafts, comprising the steps of: forming a plurality of metal tubes and cutting each said tube to a predetermined length, forming rifling on the interior surface of said metal tube extending throughout the length thereof, working said metal tubes to form a butt section having a given outer diameter and a plurality of alternating, longitudinally extending, parallel lands and grooves on the interior surface, a tip section having a given outer diameter smaller than said butt section diameter and having a plurality of alternating, longitudinally extending, parallel lands and grooves on the interior surface, and a tapered section joining said butt section and said tip section, to form a plurality of blanks;   determining the stiffness of said blanks by measuring the natural frequency thereof and selecting a set of blanks having matched natural frequencies;   forming successive blanks in said set by removing an amount from the tip section of each blank of a set of blanks, the removed amount increasing for each said successive blank by a constant increment such that said resulting set of shafts includes members varying in length by said constant increment so that said set of said successive length shafts represents a set of golf club shafts having matched frequencies along a predetermined gradient.   
     
     
       13. A method according to claim 12, wherein said predetermined blank length is 44 inches and said tapered section is 24 inches. 
     
     
       14. A method according to claim 12, wherein prior to working said tubes have a constant outer diameter, and removing a predetermined length from the butt section of each blank of said set of blanks, said removed butt length being constant for each successive blank in the set. 
     
     
       15. A method according to claim 12, wherein prior to working said tubes have a constant outer diameter, and wherein each blank used to produce said set of golf club shafts has substantially the same matched natural frequency of plus or minus two cycles per minute. 
     
     
       16. A method according to claim 15, wherein each shaft of said set of golf club shafts has a predetermined kick point. 
     
     
       17. A set of frequency matched shafts, comprising; a plurality of shafts varying in successive lengths by a constant increment and each comprising a butt section having a continuous exterior surface of a given outer diameter and having a plurality of alternating, longitudinally extending, parallel lands and grooves on an interior surface, a tip section having a continuous exterior surface of a given outer diameter smaller than said butt section diameter and having a plurality of alternating, longitudinally extending, parallel lands and grooves on an interior surface, and a tapered section joining said tip section and said butt section, the butt section of each shaft of said set being a constant length, the tip section of each shaft varying in length successively from the prior length shaft in said set by said constant increment.   
     
     
       18. A set of frequency matched shafts as set forth in claim 17, wherein said tapered section has a gradually changing diameter between said tip section and said butt section. 
     
     
       19. A golf club shaft, comprising: a tubular blank having a continuous cylindrical exterior surface, and an interior surface, a butt section having a given outer diameter, a tip section having a given outer diameter smaller than the outer diameter of the butt section, a tapered section interconnecting the butt and tip sections, and metallurgically formed rifling comprising lands and grooves on the interior surface of the blank extending throughout the entirety of said butt, tip and tapered sections, said lands and grooves in said butt section being parallel to each other, and said lands and grooves in said tip section being parallel to each other.   
     
     
       20. A golf club shaft according to claim 19, wherein the butt and tip sections have a common central longitudinal axis and wherein the alternating longitudinally extending lands and grooves in the butt and tip sections are parallel to the common central longitudinal axis. 
     
     
       21. A golf club shaft according to claim 20, wherein the longitudinally extending lands are equally spaced apart and the longitudinally extending grooves are equally spaced apart at any given diameter. 
     
     
       22. A golf club shaft according to claim 20, wherein the metallurgically formed rifling includes at least eight lands and at least eight grooves extending throughout the entirety of the butt, tip and tapered sections.